There has been proposed an airless tire that is structured such that a cylindrical tread ring having a ground-contact surface and a hub to be fixed to an axle shaft are coupled by a plurality of radially arranged spoke plate members (for example, refer to Patent Document 1).
In the airless tire of this structure, conventionally, the spoke plate members are arranged along a tire axial direction. Accordingly, the ground-contact time of the spoke plate members becomes short, and a load on the axle shaft largely varies between when the spoke plate members are in contact with the ground and when the portions between the spoke plate members are in contact with the ground. This causes a problem of deteriorated vibration performance.
As illustrated in FIG. 9, the inventor of the present invention thus have proposed that spoke plate members (a) be inclined relative to the tire axial direction so that the ground-contact time of the spoke plate members (a) can be increased to improve vibration performance. Unfortunately, when the flat spoke plate members (a) are inclined relative to the tire axial direction, spoke length (bs) on the outer edge side in the tire axial direction becomes longer than spoke length (bc) on the central side in the tire axial direction as illustrated in FIGS. 10A and 10B as a plan view and a side view of the spoke plate member (a), respectively. That is, the spoke length does not become uniform at an arbitrary position in the tire axial direction. FIGS. 10A and 10B illustrate the spoke plate members (a) with a thickness of zero for the sake of convenience.
Accordingly, at the time of rolling, in one spoke plate member (a), a portion with a longer spoke length becomes more largely distorted than a portion with a shorter spoke length, and stress concentrates on the portion with a longer spoke length. This causes another problem that the portion with a longer spoke length breaks to decrease the lifetime of the tire.